Field of the Invention
The invention lies in the printing field and related paper handling systems. Specifically, the invention relates to an apparatus for forming stacks from a stream of successive sheets. A geometric pivot axis is defined at a predetermined level, oriented crosswise to the direction of the stream, and formed by means of rotary bearing parts. A stop face configuration is located substantially above the geometric pivot axis and is pivotable with respect to the geometric pivot axis between a working position that stops the sheets and a position pivoted away from it. The invention also pertains to a delivery system in a sheet-fed printing press that is equipped with the stack forming apparatus.
Apparatuses of this type are known for instance in sheet-fed printing presses that are commercially available from Heidelberger Druckmaschinen AG of Germany (model number SM102). Here the geometric pivot axis is formed by the longitudinal axis of a stop shaft that is connected to stops in a manner fixed against relative rotation and that with respect to the stops pivoted into their vertical working position is located at the lower end of these stops. The system comprising the stop shaft and the stops thus has a "bottom" stop shaft. The stops form a stop face configuration, which serves to stop the leading edges of the sheets that are downstream in terms of the stream of sheets and to align them in a stack.
In modern printing presses, the aforementioned stream of successive sheets is not interrupted even if a "finished" stack formed of the sheets is taken out of range of the printing press where the stack was formed--from the delivery system of the printing press--in order to make space for forming the next stack. The "finished" stack, depending on the stacking mode, may be a homogeneous configuration--composed exclusively of sheets stacked on one another--resting on a stack underlay in the form of a pallet, or a so-called cradle stack. In a cradle stack a further stack underlay rests on posts that are seated on a previous stack underlay, and a partial stack whose height is less than that of the posts rests on a given stack underlay, and in which so-called cradle boards are used as a given stack underlay, of which the board carrying the lowermost partial stack rests in turn on a pallet, for instance.
The total height of the "finished" stack is dimensioned such that, depending on the design of the printing press, it can be fed out of the delivery system in the direction of travel of the sheets through the printing press or in a direction crosswise to it. Meanwhile, other sheets arriving from the stream, depending on the stacking mode, are deposited on a further board or cradle board set down on an empty pallet as operation continues, or on an auxiliary stack carrier, particularly in the form of a rake, that temporarily carries a certain number of sheets. From the auxiliary stack carrier, as operation continues, an auxiliary stack formed on it is transferred to a further stack underlay in the form of a pallet.
It will be understood that the applicable further board or cradle board or rake, during stack formation on a previous board or cradle board or a previous stack underlay in the form of a pallet, is located outside the stream of sheets and must be moved into this stream if it is to be used as intended. This is done in a region of the stream of sheets in which the sheets are moving downward while being oriented essentially horizontally, while they move at a defined deposition speed toward the stops, specifically by horizontal insertion of the respective board, cradle board or rake between two successive sheets. The trailing sheet is prevented from moving downward, at least for the duration of the insertion, at one end of the sheet pointing counter to the direction of the insertion, by means of a sheet catcher or so-called sheet upholder. To this end, the sheet upholders are also brought out of an outset position, where they are located outside the stream of sheets, into the stream for the aforementioned length of time and are then returned to their outset position immediately after the insertion of the further board, cradle board or rake has been completed. The insertion is typically done the stack, which at that time is located below the sheet catcher, is lowered by an amount determined such that the further board or the further cradle board or the rake can be inserted without contacting the topmost sheet of the stack.
In the event that a further board or the rake has been inserted, the stack then located under the sheet catcher is a finished stack, which can then be transported out of the delivery system. Once the finished stack has been transported out of the delivery system, a further stack underlay should be moved into the delivery system and lifted, by a main stack lifter, to a level at which the board, with a partial stack formed on it in the mean time, or a partial stack formed in the meantime on the rake, can be taken over by the further stack underlay. The aforementioned partial stack can by that time, depending on the thickness of the sheets and the speed with which the sheets succeed one another, attain a more or less great height. This circumstance is typically addressed with an auxiliary stack lifter, by means of which guides that receive the further board or the rake are adjustable in height between an insertion level, at which the insertion as described takes place, and a lower level than the insertion level, at which lower level the aforementioned takeover by the further stack underlay takes place.
The auxiliary stack lifter initially keeps the aforementioned guides, and thus the inserted further board or rake, at the insertion level, specifically until a topmost sheet of a partial stack, now being built up on the further board or on the rack, has regained the production level, at which the sheets are deposited on the lowered stack before the stack is lowered. The time required for this is available then for transporting the lowered stack out of the delivery system, because the auxiliary stack lifter lowers the further board or the rake in proportion with the cadence of the successive sheets, so that the aforementioned production level is now maintained.
In the event that a further cradle board has been inserted, the stack located below the sheet catcher is either a finished cradle stack intended for transport out of the delivery system, or a cradle stack which has not yet reached its intended total height but whose topmost partial stack has reached its respective maximum height.
Regardless of whether the cradle stack is a finished stack or a still unfinished stack, the insertion of a further cradle board and its support in turn on posts set on a preceding cradle board, or its takeover by a platform raised by the main stack lifting mechanism requires a certain amount of time, within which, just as in the case described where a further board or the rake has been inserted, a partial stack of a certain height can form on the further cradle board, so that once again a lowering of the further cradle board adapted to the cadence of the successive sheets is appropriate, once the topmost sheet of the partial stack has reached the aforementioned production level.
Regardless of the stacking mode, this lowering is now one of the reasons why the rake or a further board or cradle board is typically inserted into the stream of sheets below the stop shaft mentioned at the outset. But then, no matter how close together the stop shaft and the rake, for instance, are, there is a region in which the stop faces, pointing upward in their working position relative to the stop shaft, of the stops carried by the stop shaft exert no orienting effect on the leading edges of the sheets. It is in fact possible for individual sheets of the partial stack forming on the rake to slip into a gap between the rake and the stop shaft.
In the above-mentioned printing presses sold by Heidelberger Druckmaschinen, model number SM102, this nuisance is counteracted by means of strippers, which are positioned on the stop shaft wherever a bar of the rake, inserted counter to the direction of travel of the sheets through the printing press, is located below the stop shaft. These strippers are wedge-shaped and rest with the tip of the wedge on a given rake bar and thus close the aforementioned gap between the rake and the stop shaft.
If a pallet provided with grooves, in such a way that the partial stack can be lifted from the rake by means of the pallet that can be raised with the aid of the main stack lifter is used as a further stack underlay--to take over the partial stack formed on the rake--then the partial stack upon extraction of the rake from its position below the partial stack remains untouched thereby, so that the aforementioned wedgelike strippers make a sufficient contribution to forming an overall flat face end of a given stack in a so-called nonstop operating mode of a delivery system.
From German Patent DE 29 35 710 C2, it is also known, in a delivery system operating in the nonstop mode and embodied with a rake for temporarily carrying a partial stack formed on it, in which the rake is inserted into the stream of sheets in the direction of sheet travel through the printing press, to dispose stops on a face end of the stack located upstream in terms of the direction of sheet travel through the printing press, whose stop faces point downward with respect to a stop shaft that carries the stops. The rake bars, embodied here in the form of telescoping tubes, are located, when they gave been inserted into the stream of sheets, in gaps between the stops, so that for the edges of the sheets oriented toward these stops, a corner is formed that is quasi-closed, because it is impenetrable on the one hand by the rake bars and on the other by the stop faces.
Such stop systems--with a stop shaft located at the top--are inferior, however, to the stop system with the bottom stop shaft mentioned at the outset, because they involve the risk of shifting of the associated side of the stack toward the stop faces. Specifically, the stacking of sheets on one another takes place below the stop shaft, while conversely in systems with a bottom stop shaft this process takes place above it and thus each stack layer in the course of the aforementioned lowering of the stack, which is adapted to the cadence of the successive sheets, moves past the stop faces in a region thereof where because of their closeness to the stop shaft they form a relatively rigid configuration. This is not the case, however, in stop systems with a stop shaft located at the top.